We are seeking to identify the cause of cerebral vasospasm following the rupture of intracranial aneurysms. Vasospasm is a serious and distinct entity with frequent disastrous consequences due to cerebral ischemia, edema and infarction. Because of it, surgeons must often delay operations or risk postoperative infarction; to delay, however, invites re-bleeding. We believe that the factors responsible for vasospasm are contained in blood and released into cerebral spinal fluid at the site of subarachnoid hemorrhage. During the past two years, we have implicated monoamines contained in blood or brain in the vasoactive process. We wish to continue this inquiry in order to develop a rational basis for therapy. We also wish to continue a double-blind clinical study to prevent postoperative cerebral vasoconstriction and infarction, that has been in progress for the last 10 months at four teaching hospitals in Boston.